It is well known that an aromatic primary amine color developing agent is oxidized with an exposed silver halide as an oxidizing agent and the thus oxidized developing agent is reacted with a coupler to form an indophenol dye, an indoaniline dye, an indamine dye, an azomethine dye, a phenoxazine dye, a phenazine dye or an analogue thereof to thereby obtain a color image.
Most of the conventional magenta color image forming couplers which have widely been put to practical use and also intensively studied are 5-pyrazolone couplers. The 5-pyrazolone couplers are excellent in color formation rate and efficiency and azomethine dyes formed therefrom exhibit excellent fastness to light and heat. It is known, however, that these couplers show unfavorable absorption of yellow components in the vicinity of 430 nm, that should cause poor color reproduction.
Magenta color image forming skeletons so far proposed to reduce the yellow components include a pyrazolobenzimidazole skeleton as described in British Pat. No. 1,047,612; a pyrazolotriazole skeleton as described in U.S. Pat. No. 3,725,067; a pyrazoloimidazole skeleton as described in U.S. Pat. No. 4,500,630; a pyrazolopyrazole skeleton as described in Japanese Patent Application (OPI) No. 43659/85 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"); and a pyrazolotriazole skeleton as described in European Pat. No. 119,860A.
Any of the dyes formed by these couplers is superior to those formed by the conventional 5-pyrazolone couplers in terms of freedom from unnecessary absorption of yellow components. Further, these proposed couplers are advantageous for color reproduction in that the absorption in the longer wavelength side of an absorption spectrum sharply becomes zero.
The present inventors have found, however, that these pyrazoloazole couplers also possess unfavorable properties as set forth below in spite of their superiority.
When these couplers coexist with silver halides that are necessary as oxidizing agents for an aromatic primary amine developing agent to cause a color reaction, more specifically, when an emulsion of these couplers and a silver halide emulsion are mixed to prepare a coating composition, examination of the photographic properties revealed that the sensitivity, gradation and fog inherent in the silver halide emulsion used are not manifested, and the silver halide emulsion, in some cases, undergoes sensitization or densitization or suffers from reduction in color density. This behavior of the silver halide emulsion can be confirmed by making a comparison with the results obtained by color development or black-and-white development of a photographic material using 5-pyrazolone couplers under the same conditions. A part of the behavior can also be proved by comparing the results obtained by black-and-white development of a photographic material containing the silver halide emulsion alone without using any coupler.
Couplers to be used in silver halide color photographic materials are not essentially expected to exert any influence on silver halide emulsions except for development inhibitor-releasing couplers or development accelerator-releasing couplers. In particular, it is not favorable that the couplers have any influence upon the light-sensitive mechanism to induce sensitization or desensitization.
The above-described influences on silver halides are scarcely noted in the 5-pyrazolone couplers having been broadly employed as magenta color image-forming couplers, but are widely observed among the pyrazoloazole couplers. Therefore, in order to fully and practically utilize excellent hues developed by the pyrazoloazole couplers, it is highly beneficial to exclude all the aforesaid influences on silver halides.